As said in the title, I want to romance Kaidan in the first game. Since it isn't possible in a normal play, I'm afraid the save file may get corrupted so I can't play my old Shepard if I import it into ME2 and ME3; or it can be imported but their relationship is gone. Maybe Bioware didn't prepare the lines for such scenario and they say something strange when they reunite. If any of these situations happen, I think I would consider delaying the romance until the third game.
Whenever a love interest related dialog comes up you will get the same dialog female/male Sheppard would get. This usually happens if you edit romances via save game editors that are gender exclusive like Kaidan who used to be exclusively for female player characters